Cnidarians are known to from very complex colonies. Coral reefs are large, complex communities made up of many polyps, which are usually clones of each other. A new study; however, has shown an even more impressive level of organization among a fellow cnidarian. Nanomia bijuga as it’s called is a species of jellyfish in which individuals can organize themselves into groups based on age and work together to propel themselves through the water.
N. bijuga is part of a group called physonect siphonophores. Physonects are composed of several genetically identical clones called nectophores that make up the colony. The nectophores are responsible for the propulsion of the colony.
The team of researchers found out that the older, larger nectophores are located at the rear of the propulsion unit called the nectosome. This makes sense because the older nectophores can provide much stronger propulsion. Young nectophores are born at the top to the nectosome. While they cannot provide enough propulsion to push the colony forward, they can steer the colony. They can act as a form of lever by pushing water away at the top of the nectosome where it is much more efficient than at the bottom where the ‘engine’ is.
As the young nectopohores age and become bigger, they slowly migrate towards the rear of the nectosome where they become the engine and new nectophores are born to replace them.
Nanomia bijuga colony. The numbered circles are nectophores. They comprise the nectosome that is labelled. Nectophores 3-13 are larger and push the colony forward and the 1 and 2 are smaller and steer the colony. New nectophores are formed at the nectophore bud zone.
Using this method of movement, N. bijuga colonies can travel remarkable distances. The typical nectosome consisting of about 13 nectophores is about 2 centimetres long but can travel a distance of 200 metres in a day. Put on a human scale, this is equivalent to not only running a marathon a day, but doing so carrying the weight of another human on your back. Their fast movement has allowed these species to occupy a large portions of oceans.